In a so-called drum type (or a front loading type) spin extractor, wet laundry after being washed are thrown into a basket drum having a horizontal rotation axis from the front opening, and the drum is rotated about the horizontal axis at high speed. When, in the spin extractor of this type, the drum is rotated at high speed with the laundry distributed unevenly therein, abnormal vibration occurs due to the uneven mass distribution around the axis. In conventional washing machines that include such a drum type spin extractor, one or several heavy weights are attached to the tub enclosing the drum for suppressing such an abnormal vibration. This naturally increases the weight of the washing machine, which makes the transportation and more installation difficult.
Several proposals have been made addressing this kind of abnormal vibration of the drum type spin extractors. In the Publication No. H6-254294 of Japanese Unexamined Patent Application, a spin extractor is disclosed in which the laundry is evenly redistributed in the drum by rotating the drum at low speed before rotating it at high speed for extraction. The process in detail is as follows. First the drum is rotated at a very low speed for a very short time, and then it is rotated at a low speed which is a little higher than said very low speed but quite lower than the speed for liquid extraction. By the two-stage rotating operation, the laundry in the drum is redistributed. And the machine is equipped with a vibration sensor on its base. When the sensor detects vibration while the drum is rotated at high speed for extraction, the speed of the drum is lowered.
In the above spin extractor, it is not assured that the laundry is redistributed evenly with a single low-speed rotating operation. If vibration is detected by the sensor when the drum is rotated at high speed for extraction after the low-speed rotating operation, another trial of low-speed rotating operation is necessary to redistribute the laundry. It may take a long time before a thoroughly even distribution is obtained if such trials are repeated several times.
Another disadvantage of the above spin extractor is that an even distribution in the drum is impossible if the laundry in the drum is a single article and is heavy, for example jeans. In this case, vibration cannot be suppressed by the above method.
In the Publication No. H7-100095 of Japanese Examined Patent Application, a spin extractor is disclosed that adjusts the rotating balance using a weight piece attached on a part of the inner wall of the drum. It is assumed in the spin extractor that, while rotated at low speed, the drum is balanced when the weight piece is at the top because the laundry in the drum rests at the bottom naturally because of the gravity, at which time the drum is started and rotates at high speed for extraction.
The complete balancing of the drum is not assured, however, because the weight of the laundry is not always equal to the weight of the weight piece. It is of course possible to balance the weights if the weight of the laundry thrown in the drum is strictly controlled, which is unpractical in actual use of a spin extractor.